The present invention concerns apparatus for controlling a vacuum actuated device which adjusts the closing limit of a carburetor throttle valve of a motor vehicle internal combustion engine of the type in which the fuel-air mixture is supplied to the engine intake manifold. The invention is applicable to motor vehicles equipped with an automatic transmission capable of being shifted in response to signals produced by a hydraulic transmission control unit with at least one governor supplying a speed-dependent pressure. A control valve, arranged in the vacuum line extending from the intake pipe or manifold of the internal combustion engine to the aforementioned closing adjustment mechanism is actuated as a function of the driving speed of the vehicle.
In order to decrease the emission of noxious substances during deceleration operation of motor vehicle (automobile) engines of the aforementioned type, a technique is known whereby the carburetor throttle valve is opened sufficiently widely, during this operation state, to supply an adequate quantity of air for combustion of the fuel which reaches the combustion chambers. This throttle valve position is customarily achieved by means of a vacuum-actuated device that receives vacuum through a connecting line from the intake pipe or manifold of the engine.
A vacuum of approximately 370 mm Hg in the intake pipe is normally required for optimal combustion during deceleration operation of an automobile engine. However, this vacuum level is less than the normal idling vacuum of approximately 400 mm Hg so that, during idling, the throttle valve-controlling vacuum actuated device would tend to open the throttle slightly, and thereby increase the speed of the engine, if measures were not taken to prevent this from occurring. It is known from the German patent publication (DOS) No. 2,046,436 to cut off the intake vacuum to the vacuum-actuated device at low vehicle speeds. To this end the vacuum line leading from the intake pipe to the vacuum-actuated device is provided with an electro-magnetically-actuated (solenoid) control valve which is switched as a function of vehicle speed by a relatively costly electronic circuit.
An object of the present invention is to provide apparatus, distinguished by low manufacturing cost and high reliability, for controlling the closing limit of a carburetor throttle valve for motor vehicles having an automatic transmission.